linux-kernel - [PATCH v6 07/39] mm: clarify __GFP

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Message-Id: <cdffde013973c5634a447513e10ec0d21e8eee29.1643047180.git.andreyknvl@google.com>
Date:   Mon, 24 Jan 2022 19:02:15 +0100
From:   andrey.konovalov@...ux.dev
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrey Konovalov <andreyknvl@...il.com>,
        Marco Elver <elver@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH v6 07/39] mm: clarify __GFP_ZEROTAGS comment

From: Andrey Konovalov <andreyknvl@...gle.com>

__GFP_ZEROTAGS is intended as an optimization: if memory is zeroed during
allocation, it's possible to set memory tags at the same time with little
performance impact.

Clarify this intention of __GFP_ZEROTAGS in the comment.

Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>

---

Changes v4->v5:
- Mention optimization intention in the comment.
---
 include/linux/gfp.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 80f63c862be5..581a1f47b8a2 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -232,8 +232,10 @@ struct vm_area_struct;
  *
  * %__GFP_ZERO returns a zeroed page on success.
  *
- * %__GFP_ZEROTAGS returns a page with zeroed memory tags on success, if
- * __GFP_ZERO is set.
+ * %__GFP_ZEROTAGS zeroes memory tags at allocation time if the memory itself
+ * is being zeroed (either via __GFP_ZERO or via init_on_alloc). This flag is
+ * intended for optimization: setting memory tags at the same time as zeroing
+ * memory has minimal additional performace impact.
  *
  * %__GFP_SKIP_KASAN_POISON returns a page which does not need to be poisoned
  * on deallocation. Typically used for userspace pages. Currently only has an
-- 
2.25.1